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The selection principles should be based on the requirements of the operating conditions; it is necessary to take into account both the shape of the head and the pattern of stress distribution, as well as the difficulty of stamping, welding, and assembly, in order to conduct a comprehensive technical and economic analysis. In terms of geometry, for the same volume, the hemispherical head has the smallest surface area, while the elliptical head is roughly the same as the disc-shaped head. In terms of mechanics, under the same conditions of diameter, wall thickness, and operating pressure, the hemispherical head experiences the least stress; the stress in biaxial membranes is equal and distributed evenly along the meridians. When connected to a cylinder with the same wall thickness, the maximum stress near the edges differs little from the stress in the membranes. The stress distribution in an elliptical head is not as uniform as that in a hemispherical head, but it is better than that in a disc-shaped head. The stress is highest at the apex, while circumferential compressive stress occurs at the equator. When connected to a cylinder with a wall thickness equal to Di/(2h) = 2, an elliptical head can achieve strength equivalent to that of the cylinder. The greatest mechanical drawback of disc-shaped end caps is their small fold radius r; the presence of this folded area causes discontinuity in the meridians of the end cap, resulting in high meridional bending stresses and circumferential compressive stresses in that area. However, the smaller the r/R value, the greater these stresses in the folded region become, which may lead to circumferential cracks as well as circumferential wrinkles. When r=0, the dish head becomes a flangeless spherical cover; its mechanical properties are poor, with peak stresses occurring in the local area at the fold point. The weld at that fold point becomes a source of risk, and the fillet welds between the head and the cylinder are of full-penetration design. Conical end caps are used in chemical containers because the conical shape facilitates even distribution of fluids and efficient discharge. In terms of mechanical properties, the tip portion of the cone has high strength, and reinforcement is generally not required for the openings at this tip. In terms of manufacturing and material consumption, various types of end caps are generally produced by hammering, stamping, rolling, or explosive forming. Hemispherical and elliptical end caps are usually manufactured by stamping; large hemispherical end caps can also be first stamped into spherical segments before being assembled and welded together. Disc-shaped end caps are typically made by hammering, stamping, or explosive forming, with the folded edges being formed either by rolling or hammering. From a manufacturing process perspective, the deeper the head, and the larger its diameter and wall thickness, the more difficult it is to manufacture, especially when high-strength steel is used. Overall, stamping hemispherical heads is less feasible to manufacture than elliptical heads. An oval head must be manufactured using a geometrically accurate oval-shaped mold through manual hammering. Elliptical end caps offer great manufacturing flexibility, while it is difficult to form the tip portion of conical end caps. When the apex angle is small, in order to avoid manufacturing difficulties and reduce the height of the cone, composite end caps (such as those with a spherical apex) can sometimes be used.